Critical soil Olsen-P and phosphorus-use efficiency in four wheat cultivars: Evidence from the Sawyers I long-term experiment at Rothamsted

Context and objective Critical Olsen-P levels underpin phosphorus (P) management in UK wheat, yet the recent global cereal threshold of 17.1 mg kg −1 Olsen-P has not been benchmarked against UK long-term field experiments with cultivar-level resolution. We aimed to determine the critical Olsen-P for optimum grain yield in four wheat cultivars, quantify genotypic variation in P-use efficiency (PUE), and benchmark the estimates against the global cereal consensus. Methods The Sawyers I experiment at Rothamsted was sampled over three seasons (2011/12–2013/14) across twelve target Olsen-P levels (3–60 mg kg −1 ) and four cultivars representing approximately sixty-five years of wheat breeding (1946–2010) and two NABIM end-use classes (three bread-making, two of them NABIM Group 1, and one Group 4 hard feed). Mixed-effects models in R were independently reproduced by a separate REML analysis in Genstat. Critical Olsen-P was estimated at 95% of maximum yield by linear interpolation of estimated marginal means. Results and conclusions Critical Olsen-P ranged from 18.1 to 21.9 mg kg −1 (mean 19.6 ± 1.66) and was reproduced by Genstat within 1 mg kg −1 per cultivar (mean difference 2.3%). No cultivar × P interaction was detected. The modern Group 4 feed cultivar Conqueror (c. 2010) yielded 20% more grain than the 1964 Group 1 bread-making cultivar Maris Widgeon across the P gradient, despite equivalent P offtake (27.0 vs 26.6 kg P ha −1 ; p = 0.85) and similar partitioning (Harvest P Index ∼ 0.86). This advantage was associated with greater internal P-utilisation efficiency (grain-P dilution) rather than enhanced P acquisition; because breeding era, growth habit and end-use class are confounded in this four-cultivar panel, it cannot be attributed to breeding alone. The critical Olsen-P (19.6 mg kg −1 ) is consistent with the consensus for global cereals and lies in the lower half of the UK ADAS Index 2 range (16–25 mg kg −1 ). Significance Maintaining soil P at the lower half of ADAS Index 2, combined with high-efficiency cultivars, offers a practical strategy to reduce fertiliser inputs and P losses without compromising yield. Cultivar choice therefore represents an additional lever for improving system-level P-use efficiency.